In vitro evaluation of antibiotic elution from polymethylmethacrylate (PMMA) and mechanical assessment of antibiotic-PMMA composites

OBJECTIVE: To determine whether different methods of sterilization of antibiotic vials or the heat of polymerization altered the antimicrobial activity or mechanical properties of antibiotic/polymethylmethacrylate (PMMA) composites when compared to antibiotic-free PMMA. STUDY DESIGN: In vitro study. METHODS: Steam-sterilized, gas-sterilized, and non-sterilized 1 gram vials of cefazolin and injectable gentamicin sulfate (high and low doses) were mixed with PMMA to prepare composites for antibiotic elution evaluation, compression, and elongation testing. Blocks of PMMA that contained antibiotic were assayed for antibacterial activity using an agar gel diffusion method or were placed in phosphate buffered saline (PBS) to assess elution of antibiotic. Phosphate buffered saline samples from steam-sterilized cefazolin and high-dose gentamicin groups were assayed on days 1, 2, 5, and 9 for cefazolin or gentamicin concentration by high-pressure liquid chromatography or fluorescent polarization immunoassay, respectively. RESULTS: PMMA blocks containing antibiotic inhibited bacterial growth of Staphylococcus aureus 25923 for an average of 9 days. Cefazolin and gentamicin concentration in PBS decreased dramatically after the first 24 hours, but remained above minimum inhibitory concentration (MIC) throughout the experiment for all groups except low-dose gentamicin. Compressive strength of plugs made from plain cement and plugs made from PMMA mixed with untreated and steam-sterilized cefazolin was similar, but was significantly different from the other groups. There appeared to be an inverse relationship between compressive strength and elongation. CONCLUSION: PMMA/antibiotic composites inhibited bacterial growth for 7 to 10 days. Compressive strength was affected by different additions of antibiotic. CLINICAL RELEVANCE: Bacteria introduced during a surgical procedure may be inhibited by elution of antibiotic from PMMA at the time of contamination.     

In vitro elution of gentamicin, amikacin, and ceftiofur from polymethylmethacrylate and hydroxyapatite cement

OBJECTIVE: To compare the elution characteristics of ceftiofur and liquid and powdered gentamicin and amikacin from polymethylmethacrylate (PMMA) and from hydroxyapatite cement (HAC). METHODS: PMMA and HAC beads in triplicate were impregnated with various amounts and formulations of antibiotics. Beads were immersed in 5 mL of phosphate buffered saline that was replaced at 1, 3, 6, and 12 hours, and 1, 2, 3, 5, 7, 10, 14, 18, 22, 26, and 30 days. The eluent was stored at -70 degrees C until assayed within 2 weeks by microbiological assay (gentamicin and amikacin) or capillary electrophoresis (ceftiofur). RESULTS: Rate of elution for all beads was greatest within the first 24 hours. Cumulative release of total antibiotic dose from beads over 30 days was significantly greater from HAC than PMMA. Antibiotic elution was directly related to the amount of antibiotic incorporated into the cement. Powdered and liquid forms of gentamicin had similar elution rates from PMMA. Elution of amikacin from PMMA beads was greater when the powdered form was used compared with liquid amikacin. Eluent concentrations of ceftiofur were similar to those of the aminoglycosides during the first 3 to 7 days but then decreased precipitously by comparison. CONCLUSIONS: Elution of antibiotics from HAC was greater than from PMMA. Gentamicin- and amikacin-impregnated PMMA and HAC released bactericidal concentrations of antibiotic for at least 30 days. Ceftiofur-impregnated PMMA or HAC is unlikely to provide long-term bactericidal concentrations. CLINICAL RELEVANCE: Gentamicin and amikacin elute effectively from PMMA and HAC.     

Elution profiles of cefazolin from PMMA and calcium sulfate beads prepared from commercial cefazolin formulations

Antibiotic beads have become popular for the treatment of local bacterial infections. The preparation of antibiotic beads from commercial pharmaceutical antibiotics is a convenient method in clinic. The elution characteristics of cefazolin from polymethylmethacrylate (PMMA) (SmartSet HV, Depuy I and Cemfix 3) beads and calcium sulfate beads were studied. Commercial cefazolin formulation was incorporated in PMMA or calcium sulfate at 1 g cefazolin/10 g of matrix substances to form beads. The concentrations of eluted cefazolin during 15 days were greater than MIC for Staphylococcus aureus (ATCC 25923). The eluted cefazolin concentrations were in the range of 3.6 ± 1.2 to 4.6 ± 0.4 mg for PMMA beads and 15.4 ± 1.7 mg for calcium sulfate beads. The accumulated eluted cefazolin from PMMA beads and calcium sulfate beads for 15 days were 34.41 ± 3.93 to 38.67 ± 3.04% and 95.94 ± 3.93%, respectively. The various storage conditions; at room temperature or 4°C, with or without light-protection, for 6 months had little effects on the amounts of eluted cefazolin. The results showed both in-housed cefazolin-PMMA beads and cefazolin-calcium sulfate beads could be the effective tools for the treatment of local bacterial infections.     

In vitro elution of gentamicin from Plaster of Paris beads

OBJECTIVE: To determine the in vitro elution characteristics of gentamicin from Plaster of Paris-gentamicin (POP-gent) beads. STUDY DESIGN: In vitro, controlled, experimental study. METHODS: The POP-gent beads were made using a bead mold from 20 g calcium sulfate hemihydrate, 5 mL (500 mg) gentamicin solution, and 3 mL of phosphate buffered saline (PBS). Control beads were made similarly, using 30 g of dried powder and 8 mL of PBS. Beads were left in the mold overnight, gas-sterilized with ethylene oxide, and stored at room temperature for 5 months before testing. Bead chains were placed in sterile tubes containing porcine serum, and tubes were placed in a 37 degrees C incubator on a rocker. Serum was removed at intervals over 14 days and the concentration of gentamicin determined by fluorescent polarization immunoassay. Serum antibacterial activity was determined against an equine origin Escherichia coli. RESULTS: POP-gent beads released gentamicin for the 14-day sampling period. Eighty percent of the gentamicin incorporated in the beads was released over the first 48 hours. Eluent from POP-gent beads inhibited the growth of E coli at all time periods. No gentamicin was eluted from control beads and control eluent did not inhibit growth of E coli. CONCLUSIONS: In this experimental model, POP-gent beads released bactericidal drug for 14 days. Eighty percent of the gentamicin incorporated into the beads was released during the first 48 hours. The drug retains its bactericidal activity after ethylene oxide sterilization and storage at room temperature for up to 5 months. CLINICAL RELEVANCE: Pop-gent beads may be a useful repository device to deliver gentamicin locally in tissues.     

Effects of porcine small intestinal submucosa on elution characteristics of gentamicin-impregnated plaster of Paris

OBJECTIVE: To evaluate effects of small intestinal submucosa (SIS) on elution properties of plaster of Paris (POP). SAMPLE POPULATION: 27 POP cylinders, 27 POP spheres, and 9 polymethylmethacrylate (PMMA) spheres. PROCEDURES: Pellets were loaded with gentamicin (50 mg/g) and divided into 7 groups of 9 beads each: PMMA spheres; POP cylinders coated with 0, 4, or 8 layers of SIS; and POP spheres coated with 0, 4, or 8 layers of SIS. Gentamicin concentration was measured 6, 12, 18, 24, 32, 40, and 48 hours and 3, 4, 5, 7, 14, 21, 28, 35, and 42 days after wrapping. Porosity was evaluated via scanning electron microscopy. Curvature factor of elution curves, total amount of drug released (TDR), time required to reach 50% of total release (TDR(t50)), and number of days with concentrations > or = 1 microg/mL were compared among groups. RESULTS: SIS decreased the curvature factor and increased the TDR(t50) and TDR of POP spheres and cylinders. Curvature factor of the PMMA-release curve remained lower than that for any POP group, but all POP groups wrapped in SIS released more gentamicin than PMMA spheres. Gentamicin concentrations remained > or = 1 microg/mL in SIS-wrapped POP and PMMA groups throughout the study. Wrapping POP in SIS minimized the increase in porosity of pellets. CONCLUSIONS AND CLINICAL RELEVANCE: Wrapping POP with SIS slows the release and increases the amount of gentamicin leaching from spheres and cylinders. All groups wrapped in SIS maintained antimicrobial concentrations greater than the minimum inhibitory concentration of most pathogens.     

The effect of implanting gentamicin-impregnated polymethylmethacrylate beads in the tarsocrural joint of the horse

OBJECTIVE: To determine the effect of intra-articular gentamicin-impregnated polymethylmethacrylate (PMMA) beads inserted in the equine tarsocrural joint on the synovial fluid, synovial lining, and cartilage, and to determine the peak and sustainable gentamicin concentrations in synovial fluid and plasma. STUDY DESIGN: Pharmacokinetic, cytologic, and histologic study of the effect of gentamicin-impregnated PMMA on normal equine tarsocrural joints. ANIMALS: Five healthy adult horses. METHODS: Gentamicin-impregnated PMMA bead strands (3 strands each of 40 beads, with each strand containing 100 mg gentamicin) were surgically inserted into one radiographically normal tarsocrural joint in 5 horses. Each horse had both joints flushed with 1 L of lactated Ringer's solution before bead administration. Synovial fluid total protein concentration, white blood cell (WBC) count, gentamicin concentration, synovial histology, cartilage integrity, and cartilage glycosaminoglycan (GAG) concentrations were determined. RESULTS: Gentamicin concentration (mean +/- SEM peak concentration, 27.9 +/- 2.27 microg/mL) occurred in the first 24 hours and remained above 2 microg/mL for 9 days. Gentamicin concentrations in control joints and the plasma remained below detectable levels. The synovial fluid WBC count for treated joints was increased compared with control joints for 72 hours, but was similar at day 6. The synovial protein concentration in gentamicin-treated joints remained increased for 21 days. Synovium in treated joints had diffuse synovitis, whereas control joints had less fibrovascular proliferation. Superficial cartilage erosion was present in all treated joints. There was no difference in the GAG content of treated and control joint cartilage. CONCLUSIONS: Short-term implantation of gentamicin (300 mg)-impregnated PMMA beads can provide therapeutic levels of gentamicin (>2 microg/mL) in the normal tarsocrural joint for 9 days; however, gentamicin-impregnated PMMA beads induce synovitis and superficial cartilage erosion. CLINICAL RELEVANCE: Temporary intra-articular administration of antibiotic-impregnated PMMA may be an effective way to treat septic joints that require constant high concentrations of antibiotics.     

In vitro elution studies of amikacin and cefazolin from polymethylmethacrylate

OBJECTIVE: To compare the in vitro elution characteristics of amikacin and cefazolin from polymethylmethacrylate (PMMA) alone and in combination. STUDY DESIGN: A prospective, controlled, experimental study. METHODS: Three aliquots of 6 g sterile PMMA were measured and to them added (1) 750 mg amikacin; (2) 1050 mg cefazolin; and (3) 750 mg amikacin and 1050 mg cefazolin. Ten beads of each antimicrobial/PMMA combination were placed in 5 mL phosphate-buffered saline (PBS) at pH 7.4 and room temperature with constant agitation. PBS was sampled at 15 time points between 1 hour and 30 days. Amikacin concentrations were determined by fluorescence polarization immunoassay and cefazolin concentrations by high-performance liquid chromatography. RESULTS: Amikacin and cefazolin eluted at concentrations greater than 8 and 4 times, respectively, above the minimum inhibitory concentration (MIC) for susceptible bacteria over 30 days. Co-elution of the antibiotics resulted in a greater rate and proportion of antibiotic eluted. Concentrations of amikacin and cefazolin in the co-eluted fluid were not maintained sufficiently above the MIC for selected bacteria over 30 days. CONCLUSIONS: PMMA beads of only amikacin or cefazolin-eluted concentrations greater than the MIC for selected bacteria for 30 days. Co-elution of the antibiotics at the selected doses resulted in a significantly shorter duration of elution and may not be effective for treatment of wound infection. CLINICAL RELEVANCE: Co-elution of amikacin and cefazolin from PMMA at the selected doses cannot be recommended for sustained treatment of infection.     

In vitro Elution of Amikacin and Vancomycin from Impregnated Plaster of Paris Beads

Objective: To describe in vitro elution characteristics of amikacin and vancomycin from calcium sulfate hemihydrate 98% (plaster of Paris, POP) beads and characterize eluent inhibition of Staphylococcus spp. Study Design: Experimental study. Methods: POP beads were impregnated with amikacin or vancomycin alone or in combination and then incubated alone or in combination for 84 days at 37°C in plastic tubes containing sterile phosphate‐buffered saline (PBS). Beads containing no antimicrobial served as negative control. Beads were intermittently moved to a new tube containing drug‐free PBS. Antimicrobial was measured in the eluent using a polarized fluorescent immunoassay. Eluent inhibition of Staphylococcus spp. was determined at each time point. Results: Antimicrobial release from beads was characterized by an initial rapid phase then a slower phase. Although antimicrobial release from beads occurred throughout the 84 days, most was in the first 24 hours, except for vancomycin alone. Duration of eluent inhibition of Staphylococcus spp. growth ranged from 0.5 (amikacin alone) to 56 days (vancomycin alone). Control eluent did not inhibit bacterial growth. Conclusions: Amikacin elution from POP beads was rapid, inhibiting growth for <24 hours with or without vancomycin. Vancomycin elution was slower and inhibited growth for 56 days alone or for 5 days with amikacin. Clinical Relevance: Vancomycin‐impregnated beads appear to be reasonable as a therapeutic option whereas amikacin‐impregnated POP beads and amikacin and vancomycin combinations may require further study before considering as a therapeutic option.     

In Vitro Elution and Antibacterial Activity of Clindamycin,Amikacin, and Vancomycin from R‐gel Polymer

Objective: To characterize the in vitro elution and bioactivity of 2 formulations of antibiotics in a novel, dissolvable, cross‐linked dextran polymer matrix: Formulation 1—amikacin and clindamycin (AC); Formulation 2—amikacin, clindamycin, and vancomycin (ACV). Study Design: Prospective, in vitro, experimental study. Methods: Aliquots of the antibiotic impregnated polymer were incubated in PBS buffer for 10 days. PBS was changed every 24 hours and concentrations of the antibiotics eluted into saline were quantified. Antimicrobial activity of the eluent from each sampling period was tested for growth inhibition of Staphylococcus aureus. Results: Both formulations of R‐gel^? had a rapid initial release of antibiotics within the first 24 hours and then the concentrations decreased gradually over 10 days. The concentration of amikacin, clindamycin, and vancomycin remained above the breakpoint minimum inhibitory concentration of each drug for a minimum of 9 days. No significant difference (P=.9938, P=.9843) was present in the elution pattern or total amount of antibiotic eluted from clindamycin or amikacin, respectively. Eluent from both groups demonstrated bioactivity against S. aureus for the entire 10‐day study period. Conclusions: Amikacin and clindamycin together, or in combination with vancomycin, elute from R‐gel^? effectively and at gradually decreasing concentrations for at least 10 days. The antibiotics maintained their bioactivity following polymerization and elution from the R‐gel^?.     

Effects of Oxygen Exposure and Gentamicin on Stallion Semen Stored at 5 and 15°C

This study was undertaken to investigate the effects of storage of stallion semen in a defined milk protein extender at 5 and 15°C under either anaerobic or aerobic conditions, with or without addition of the antibiotic gentamicin. Semen samples were collected from eight fertile stallions and stored for 96 h (day 0–4) and assessed daily for motility, velocity and membrane integrity (viability) using a CASA system. Samples for bacteriology assessment were taken on day 2 of storage. No significant (p > 0.05) differences in motility, velocity or viability were observed between treatments on days 0–2. On days 3 and 4, semen stored without gentamicin at 5°C had a significantly (p < 0.05) better semen quality compared with storage at 15°C without gentamicin, irrespective of oxygen exposure. On days 3 and 4, motility and velocity were greater in samples stored at 15°C with gentamicin, compared with the corresponding treatments without antibiotic (p < 0.05). This effect was also evident for viability on day 4. The decline in semen quality observed at 15°C most likely resulted from the effect of bacterial growth. Bacterial growth was the greatest in samples stored at 15°C without gentamicin, under both anaerobic and aerobic conditions (p < 0.05). Bacterial growth was inhibited by adding of gentamicin at 15°C, which accordingly reduced the decline in semen quality. Addition of antibiotic to samples stored at 5°C had no significant effect on any parameter analysed. In conclusion, storage at 15°C can be achieved by using an extender containing the antibiotic gentamicin. Storage at 5°C tended to maintain better semen quality irrespective of oxygen exposure, and did not necessitate an antibiotic treatment.     

Biodegradable Drug Delivery Systems for Gentamicin Release and Treatment of Synovial Membrane Infection

OBJECTIVE: This study investigated two biodegradable drug delivery systems (BDDS) for elution of gentamicin and elimination of synovial membrane infection. STUDY DESIGN: The effect of BDDS on control and infected synovial explants was determined. ANIMALS OR SAMPLE POPULATION: Synovial explants from four adult equine cadavers. METHODS: First, BDDS were placed in phosphate buffered saline for 14 days. Eluent was tested for gentamicin concentration (G) and bioactivity. Second, synovial explants were divided into four groups (n = 14/group): Group 1 (control); Group 2 (infected control) 405 cfu Staphylococcus aureus added at 6 hours; Group 3 (antibiotic BDDS [Ab-BDDS]) Ab-BDDS added at 24 hours; Group 4 (infected Ab-BDDS) 405 cfu S. aureus added at 6 hours, Ab-BDDS added at 24 hours. Both types of Ab-BDDS were used (n = 7/type/group). Explants were incubated in standard medium for 4 days. Medium was cultured and analyzed for (G) and hyaluronic acid concentration (HA). Explants were analyzed for viability and morphologic changes. RESULTS: The Ab-BDDS released >500 microg/mL of active gentamicin for 10 days. In Group 3, infection was eliminated within 24 hours, but histologic scores did not return to normal. Viability was significantly reduced by infection, but if eliminated, viability tended to return to normal. In Group 3, the Ab-BDDS had no significant effect on viability or (HA). Histopathologic scores were significantly higher for infected synovium. Infection, even if treated, significantly reduced (HA). CONCLUSIONS: Both Ab-BDDS eliminated infection within 24 hours. However, synovial morphology, viability and function did not return to normal. CLINICAL RELEVANCE: The Ab-BDDS may be useful for treatment of synovial membrane infection.     

The Use of Cefquinome in Equine Semen Extender

Antibiotics are commonly used in equine semen extender for conservation, if semen has to be stored cooled for a maximum of 48 hours or frozen, to eliminate pathogenic or potentially pathogenic bacteria from semen and reduce the risk of postmating endometritis. Little is known about the effect of antibiotics on spermatozoa when semen is stored over a longer period. Cefquinome, a broad spectrum antibiotic and fourth-generation cephalosporin, has been proven to be a powerful drug for the treatment of endometritis and mastitis in different species. Recently in equine studies, it was found to localize in high concentrations in the endometrium. Therefore, cefquinome was used as the antibiotic in semen extender and compared with a commercial semen extender containing gentamicin for effects on motility and membrane integrity of spermatozoa. During the breeding season, ejaculates from nine light horse stallions were collected and half of each ejaculate was stored for 48 hours in modified Kenney type semen extender containing either cefquinome or gentamicin. At 0, 24, and 48 hours, aliquots (20 μL) of the stored semen were evaluated for (progressive) motility and membrane integrity, as well as for various motility parameters by computer assisted sperm analysis. No differences (P > .05) were found in total motility or progressive motility between extenders at any time point. However, there were differences (P < .05) in velocity parameters, although the effect of velocity parameters on fertility is not clear. In general, semen parameters after storage in non-fat dried skim milk semen extender containing cefquinome are comparable with those after storage in semen extender containing gentamicin. The wider spectrum of bactericidal activity possessed by cefquinome may prove to be beneficial in some cases.     

Treatment of feline giardiasis with metronidazole

Seven cats from a single household with 17 cats were shedding cysts of Giardia species as detected by a modified zinc sulfate concentration technique. All the cats were housed individually in Horsfal isolation units for the duration of the evaluation, treatment, and follow-up monitoring. Each of the infected cats was treated with metronidazole at a dose of 22 mg per kg of body weight, twice a day, for 5 days. Post-treatment examination of four or five stool samples from each cat during the following 17 days did not reveal the presence of any giardial cysts in the treated cats. After treatment, the diarrhea either ceased or was markedly diminished. Therefore, metronidazole appears to be an effective form of therapy for feline giardiasis.     

Use of an orally administered combined sugar solution to evaluate intestinal absorption and permeability in cats

OBJECTIVE: To evaluate intestinal permeability and absorption in healthy cats in association with diet and normal intestinal microflora. ANIMALS: 6 healthy domestic shorthair cats. PROCEDURE: A sugar solution containing D-xylose, 30-methyl-D-glucose, L-rhamnose, lactulose, and 51Cr-EDTA was administered intragastrically to healthy cats, and urinary excretion of ingested sugars was determined 5 hours after administration. After the same cats had received metronidazole for 1 month, the study was repeated. A final study was performed while cats were maintained on a new diet differing in composition and processing. RESULTS: Lactulose-to-rhamnose ratios, reflecting intestinal permeability, were higher in cats, compared with values for humans or dogs, and values obtained before and after metronidazole administration (mean +/- SEM; before, 0.40 +/- 0.08; after, 0.45 +/- 0.09) were not significantly different. Intestinal absorption also was unaltered after antibiotic administration, and the xylose-to-glucose ratio was 0.70 +/- 0.03 before and 0.71 +/- 0.06 after metronidazole administration. Sugar recovery did not differ significantly while cats were maintained on canned or dry food. CONCLUSIONS AND CLINICAL RELEVANCE: Reference ranges were established for the percentage urinary recovery of orally administered D-xylose, 3-0-methyl-D-glucose, L-rhamnose, lactulose, and 51Cr-EDTA obtained after 5 hours in healthy cats. The intestines of cats appear to be more permeable than those of other species, although the normal bacterial microflora does not appear to influence the integrity or function of the feline intestine, because values obtained for the measured variables before or after antibiotic administration were not significantly different. In addition, differences were not detected when the diet was completely altered.     

Amikacin therapy for Pseudomonas cellulitis in an Amazon parrot

Amikacin sulfate, an aminoglycoside antibiotic, was used successfully to treat a case of severe Pseudomonas cellulitus in an Amazon parrot. Side effects of polyuria and polydipsia occurred, but resolved without treatment 3 weeks after the antibiotic regimen. Amikacin sulfate was given at a dosage of 0.04 mg/g of body weight, IM, twice a day, based on antimicrobial sensitivity results. Amikacin sulfate is indicated for P aeruginosa cellulitis that is resistant to gentamicin sulfate. Although it is potentially nephrotoxic, it can be used successfully in birds without permanent clinically evident renal effects.     

In vitro elution of amikacin and ticarcillin from a resorbable, self-setting, fiber reinforced calcium phosphate cement

Objective: To determine in vitro elution characteristics of amikacin and ticarcillin from fiber reinforced calcium phosphate beads (FRCP). Sample Population: Experimental. Methods: FRCP beads with water (A), amikacin (B), ticarcillin/clavulanate (C), or both amikacin and ticarcillin/clavulanate (D) were bathed in mL phosphate‐buffered saline (PBS) at 37°C, 5% CO₂ and 95% room air. PBS was sampled (eluent) and beads were placed in fresh PBS at time points 1 and 8 hours and 1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 18, 21, 25, 28, 35, 42, 49, and 56 days. Antibiotic concentration and antimicrobial activity of eluent against Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae were determined. Results: Both antibiotics eluted in a bimodal pattern. Beads with a single antibiotic eluted 20.8 ± 2.5% of amikacin and 29.5 ± 0.8% of ticarcillin over 56 days. Coelution of the antibiotics resulted in a lower proportion (AUC_0–∞) of antibiotics eluted for both amikacin (9.5 ± 0.2%) and ticarcillin (21.7 ± 0.09%). Bioassay of antimicrobial activity of the eluent (t=1, 8, and 24 hours) established reduced antimicrobial activity of amikacin from combination beads (D). Conclusions: FRCP beads with amikacin or ticarcillin/clavulanate, but not the combination, are suitable carriers for wound implantation. Clinical Relevance: Duration before complete resorption of FRCP beads in vivo should be determined before clinical use as a resorbable depot. The results of this study underscore the importance of testing drug combinations, despite success of the combination systemically, before their use in local applications.     

Methylprednisolone and gentamicin effects on hepatosplanchnic blood flow and carbohydrate metabolism in endotoxemic Yucatan miniature pigs

Conjoint therapy of a glucocorticoid and aminoglycoside antibiotic have been recommended for septic shock. These studies examined the hemodynamic and metabolic effects of methylprednisolone sodium succinate (MPSS) with and without gentamicin sulfate in a nonanesthetized model of nonseptic endotoxemia in Yucatan miniature pigs. Methylprednisolone sodium succinate alone had no effect on endotoxin-induced systemic hypotension. Endotoxemic pigs treated with MPSS in combination with gentamicin sulfate had lower mean arterial pressures than did MPSS-treated and nontreated endotoxemic pigs. Methylprednisolone sodium succinate alone and with gentamicin sulfate improved portal and hepatic venous blood flows moderately. Net hepatic lactate extraction, glucose production, and whole body [6-3H]glucose-derived rates of glucose appearance were also improved, but [6-3H]glucose-derived rates of glucose disappearance and blood lactate concentrations were increased, leading to no improvement in plasma glucose concentration. Pancreatic insulin secretion was higher in treated groups, which may have contributed to greater glucose utilization rates. Hepatic oxygen extraction efficiency was not affected by treatment, but increased in all groups to maintain hepatic oxygenation at base-line values. Although a calcium-antagonistic activity of gentamicin has been reported to synergize with endotoxin, thereby adversely affecting cardiovascular function, such effects did not complicate the metabolic response to steroid in the present studies.     

鲜牛奶中细菌的分离纯化及其药物敏感性分析

为了解鲜牛奶中细菌的分布情况及其对抗生素的敏感状况,实验对30份采自河北张家口地区某养殖场的新鲜无菌牛奶进行细菌分离鉴定,并分别用青霉素(16μg/ml)、氯霉素(32μg/ml)、克林霉素(4μg/ml)、红霉素(8μg/ml)、四环素(16μg/ml)、庆大霉素(16μg/ml)、环丙沙星(4μg/ml)、头孢噻吩(32μg/m)l进行药敏实验。结果显示30份牛奶样品中共分离得到111株菌,分别为葡萄球菌31株、沙雷氏菌14株、假单胞菌12株、芽孢杆菌11株、肠杆菌5株、不动杆菌4株、奇异变形杆菌3株、微球菌3株、巨球菌3株、肠球菌4株、其它菌21株。其中耐青霉素16μg/ml的为50株,耐氯霉素32μg/ml的为23株,耐克林霉素4μg/ml的为46株,耐红霉素8μg/ml的为37株,耐四环素16μg/ml的为38株,耐庆大霉素16μg/ml的是7株,耐环丙沙星4μg/ml的为8株,耐头孢噻吩32μg/ml的为40株。通过实验可知,细菌类型主要有葡萄球菌、沙雷氏菌、假单胞菌等;8种抗生素中,庆大霉素、环丙沙星、氯霉素的抑菌效果较好,而青霉素、克林霉素、红霉素、四环素、头孢噻吩的抑菌效果相对较差。     

The mechanism of enhanced intraphagocytic killing of bacteria by liposomes containing antibiotics

Liposomes containing aminoglycosides have been shown to enhance the killing of Brucella abortus and Staphylococcus aureus inside bovine phagocytic cells. This study examined the mechanism by which liposomes containing aminoglycoside enhance the intracellular killing of bacteria. Liposomes with entrapped aminoglycoside were found to significantly enhance the intraphagocytic killing of bacteria in bovine phagocytic cells (in vitro) when compared to free drug. Liposomes with entrapped aminoglycoside were also found to deliver significantly higher levels of aminoglycoside into phagocytic cells when compared to free drug (gentamicin) or free drug and liposomes without entrapped antibiotic. Antibiotic delivered to adherent phagocytic cells could be detected 3 days after treatment of the cells with liposomes containing aminoglycoside. No antibiotic could be detected in the supernatants of phagocytic cell cultures 3 days after treatment with liposomes containing antibiotic was only observed when the intraphagocytic bacteria were sensitive to the antibiotic entrapped in the liposomes. The rate of phagocytosis of S. aureus by cells treated with cationic liposomes (no entrapped antibiotic) did not differ from the rate of phagocytosis of control cells not treated with cationic liposomes. This study shows that the enhanced intraphagocytic killing of bacteria in bovine phagocytic cells occurs by direct delivery of entrapped antibiotic into the phagocytic cell by the liposome delivery vehicle and not by nonspecific enhancement of phagocytic cell function. Liposomes containing aminoglycoside appear to have no toxic effects on phagocytic cell function or viability in vitro.